Quantum Radar: The Atomic Revolution in Underground Imaging

Physicists harness the quantum properties of supersized atoms to create the next generation of detection technology

BLUF (Bottom Line Up Front)

Scientists at NIST and RTX have demonstrated a revolutionary quantum radar that uses laser-inflated cesium atoms instead of traditional antennas to detect buried objects with centimeter-level precision. The technology achieves 4.7 cm accuracy at 5-meter range and operates across multiple frequency bands simultaneously using a centimeter-sized atomic sensor. Commercial applications are emerging rapidly, with NASA deploying the technology for space missions, RTX developing it for underground utility detection, and researchers successfully demonstrating soil moisture monitoring with less than 0.5% error. This quantum sensing breakthrough promises to transform underground imaging, archaeological surveys, and infrastructure mapping while offering superior sensitivity and calibration stability compared to conventional radar systems.

The radar that located buried treasures in science fiction may soon become reality, thanks to a revolutionary approach that replaces conventional antennas with clouds of quantum-enhanced atoms. Researchers at the National Institute of Standards and Technology (NIST), working in collaboration with defense contractor RTX, have demonstrated a functional quantum radar system that could transform underground imaging for applications ranging from archaeological excavations to utility infrastructure mapping.

At the heart of this breakthrough lies an extraordinary feat of atomic engineering. The team uses lasers to inflate cesium atoms to nearly the size of bacteria—approximately 10,000 times their normal size. These bloated atoms, known as Rydberg atoms, become exquisitely sensitive to radio waves, essentially transforming into living antennas that can detect electromagnetic signals with unprecedented precision.

The Quantum Advantage

Traditional radar systems face significant limitations in miniaturization and spectral flexibility. They rely on large metal antennas and complex RF electronics that constrain their performance and restrict their applications. The NIST quantum radar, by contrast, replaces this bulky infrastructure with a glass cell about the size of a centimeter that contains the cesium atoms.

When incoming radio waves hit Rydberg atoms, they disturb the distribution of electrons around their nuclei. Researchers can detect the disturbance by shining lasers on the atoms, causing them to emit light; when the atoms are interacting with a radio wave, the color of their emitted light changes. This color shift serves as the detection mechanism, allowing scientists to monitor radio frequencies with remarkable sensitivity.

The quantum approach offers several distinct advantages over conventional systems. Rydberg atoms are sensitive to a wide range of radio frequencies without needing to change the physical setup, meaning a single device could potentially operate across multiple frequency bands required for different applications. Additionally, each cesium atom in their device is identical, and the radio receiver relies on the fundamental structure of these atoms, which never changes, providing inherent calibration stability that traditional systems cannot match.

Impressive Performance Metrics

In rigorous testing conducted in a specialized anechoic chamber designed to eliminate unwanted reflections, the NIST team demonstrated remarkable capabilities. They aimed radio waves at a copper plate about the size of a sheet of paper, some pipes, and a steel rod in the room, each placed up to five meters away. The radar allowed them to locate the objects to within 4.7 centimeters.

Recent advances have pushed performance even further. Researchers have demonstrated a compact prototype achieving centimeter-level ranging precision (RMSE = 1.06 cm) within 1.6-1.9 m. By synthesizing GHz-bandwidth (2.6-3.6 GHz), resolvable target separations down to 15 cm are observed under controlled sparse scenarios.

Expanding Applications Across Industries

The potential applications for quantum radar extend far beyond the initial underground imaging goals. NASA has developed multiple projects leveraging Rydberg atom technology for space-based sensing. The space agency is exploring Rydberg radar for cryospheric science processes including ice flow dynamics, ice-shelf evolution, snow accumulation mapping, and bedrock detection. The technology operates across six distinct radar bands from VHF to Ku bands, covering frequencies from 137MHz to 13.5GHz.

One of the most promising near-term applications involves soil moisture monitoring. Researchers have successfully demonstrated remote sensing of soil moisture using Rydberg atoms and satellite signals of opportunity, achieving less than 0.5% error in soil moisture inversion. This capability could revolutionize agricultural monitoring and water resource management.

The technology is also being adapted for automotive safety applications, with researchers developing Rydberg atom sensors to troubleshoot radar chips used in advanced driver-assistance systems, potentially improving the reliability and performance of collision avoidance technology.

Industrial and Defense Collaborations

The development of quantum radar represents a significant collaboration between government research institutions and private industry. RTX Technology Research Center is developing a mobile sensing platform using radar approaches based on quantum radio frequency sensing together with artificial intelligence to locate existing utility lines prior to installing underground power distribution lines, as part of the Department of Energy's ARPA-E program.

RTX's BBN Technologies is also developing compact, low-power photonic sensors under a DARPA program, using quantum states of squeezed light to minimize photon noise by suppressing quantum fluctuations, pushing detection sensitivity 16 dB below the shot noise limit.

Technical Breakthroughs and Innovations

The quantum radar field has seen rapid technical advances in 2024 and 2025. Recent research has focused on developing optically-biased Rydberg microwave receivers that eliminate the need for microwave local oscillators, making systems entirely optical and improving sensitivity.

Researchers have developed sophisticated signal processing techniques including compressive sensing algorithms specifically designed for Rydberg systems (CS-Rydberg) to suppress noise and mitigate undersampling problems, while establishing nonlinear response models that extend the linear dynamic range by over 7 dB.

From Quantum Computing to Quantum Sensing

The development of quantum radar benefits from cross-pollination with quantum computing research. Researchers have built quantum computers using Rydberg atoms as qubits, and advances in quantum sensing can potentially translate into advances in quantum computing, and vice versa. This synergy has enabled rapid progress, with researchers adapting error-correction techniques from quantum computing to improve Rydberg-atom-based sensors.

Commercial Viability and Future Outlook

While still in the prototype phase, quantum radar is rapidly approaching commercial viability. The work moves quantum radar closer to a commercial product, with researchers integrating the Rydberg receiver with the rest of the device more effectively than previous attempts.

Companies like Rydberg Technologies are now commercializing these quantum sensing capabilities, offering RF field measurement systems that span from near-DC to millimeter-wave frequencies with SI-traceable precision at the 0.1% level—more than 10 times better than classical antenna standards.

The quantum radar's unique advantages—ultra-broadband sensitivity, quantum-traceable calibration, compact form factor, and freedom from traditional antenna size constraints—position it to become a transformative technology across multiple industries. By harnessing the atoms' ultra-broad spectral response, the synthesized bandwidth can be extended well beyond the current range, enabling sub-centimeter resolution in future radar systems while preserving quantum-traceable calibration and a highly simplified front end.

As governments worldwide invest billions in quantum technologies and the field continues its rapid evolution, quantum radar represents one of the first practical applications of quantum sensing to emerge from the laboratory and approach real-world deployment. The technology promises to revolutionize how we see through the ground, into space, and beyond the limits of conventional sensing.

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